A Loop Thermosyphon Type Cooling System for High Heat Flux

Abstract

With rapid development of the semiconductor technology, more efficient cooling systems for elec-tronic devices are needed. In this situation, in the present study, a loop thermosyphon type cooling system, which is composed mainly of a heating block, an evaporator and an air-cooled condenser, is investigated experimentally in order to evaluate the cooling performance. At first, it is examined that the optimum volume filling rate of this cooling system is approximately 40%. Next, four kinds of working fluids, R1234ze(E), R1234ze(Z), R134a and ethanol, are tested using a blasted heat transfer surface of the evaporator. In cases of R1234ze(E), R1234ze(Z), R134a and ethanol, the ef-fective heat flux, at which the heating block surface temperature reaches 70˚C, is 116 W/cm 2 , 106 W/cm 2 , 104 W/cm 2 and 60 W/cm 2 , respectively. This result indicates that R1234ze(E) is the most suitable for the present cooling system. The minimum boiling thermal resistance of R1234ze(E) is 0.05 (cm 2 • K)/W around the effective heat flux of 100 W/cm 2 . Finally, four kinds of heat transfer surfaces of the evaporator, smooth, blasted, copper-plated and finned surfaces, are tested using R1234ze(E) as working fluid. The boiling thermal resistance of the blasted surface is the smallest among tested heat transfer surfaces up to 116 W/cm 2 in effective heat flux. However, it increases drastically due to the appearance of dry-patch if the effective heat flux exceeds 116 W/cm 2 . On the other hand, in cases of copper-plated and finned surfaces, the dry-patch does not appear up to 150 W/cm 2 in effective heat flux, and the boiling thermal resistances of those surfaces keep 0.1 (cm 2 • K)/W.